Background
The potential for production of biofuels from biological material has been highly acknowledged around the world during the last decade. The advantages are several, such as the high abundance of the raw material, sustainability, independence from fossil fuels and the positive impact on the global CO2 emissions. In addition to ethanol, several other chemicals can be simultaneously obtained in biorefineries in an analogous manner to the variety of products obtained from petroleum in oil refineries. A lot of the interest has focused on production of ethanol from feedstock such as sugarcane and corn. However, use of these feedstocks is somewhat problematic because it can sometimes compete with the production of food and the agricultural land use. Therefore, it is important to identify alternative or additional sources of biological material for production of biofuels. Lignocellulosic biomass has the potential to serve as feedstock for sustainable production of biofuels. In our latitudes, the obvious choice is to produce so-called second generation biofuels from the lignocellulose of the forest trees. Examples of the use of lignocellulose in biofuel production exist in Sweden even today (www.domsjoe.com) and new approaches are being developed (www.sekab.com). However, the use of the lignocellulose is challenging due to its recalcitrance i.e. resistance to the chemical and enzymatic hydrolytic treatments to deconstruct the lignocellulose into the constituent monomeric sugar units. Also, the forest industry sometimes considers biofuel production from the lignocellulose problematic due to the competition with other end uses of the woody biomass. We intend in the BioImprove programme to reduce some of the obstacles inherent in the biological material for the use of lignocellulose in bioenergy production.
Cellulose is the major biopolymer in the cell wall and makes up between 40 to 50% of wood. It is a homopolymer consisting of β-1,4-glucan chains, which participate in inter- and intra-hydrogen bonding to crystallize into cellulose microfibrils. The cellulose fibril network provides strength and rigidity to the plant cell wall and represents the supramolecular scaffold with which other wall components such as pectins, hemicelluloses and lignin are associated. Regardless of whether thermochemical or biotechnical processes, such as enzymatic hydrolysis, are used in the biorefinery, the processability of cellulose depends on whether it is crystalline or amorphous. Very little is known about the factors regulating cellulose crystallinity even though the activity of cell wall-residing cellulases, interaction of the cellulose microfibrils with the cortical microtubules, the polymerization degree of cellulose and the length of the cellulose microfibrils have been implicated. We know that cellulose is synthesized in plants by rosette-like complexes in the plasma membrane, but how the function of these complexes is controlled and how it affects the structure of cellulose is not known. With very few exceptions, analysis of mutants affected in cellulose content has suffered from inappropriate analytical tools and analyses in complex tissues instead of focusing specifically on the secondary cell walls. In this programme we will utilize the best tools available to analyse cellulose structure and crystallinity in hybrid aspen secondary cell walls in order to gain information about the control of cellulose structure, such as crystallinity, and how it affects bioprocessing properties of the wood.
Hemicelluloses, the second main type of cell wall polysaccharides, constitute about one fourth of wood biomass and are required for correct assembly of the secondary cell wall. Xylan, which is the main hemicellulose in hardwoods, is considered problematic from the biorefinery perspective and pulping, as it forms complex linkages with other cell wall components, notably lignin. Therefore, improving the separation of xylan from lignin and cellulose is one of main goals for lignocellulose improvement. This will be possible by manipulating xylan side chains, since the side chains are mainly responsible for these interactions.
In addition to the polysaccharides, the cell wall contains lignin. Lignin is a complex polymer that is highly resistant to the hydrolytic conditions during cell wall deconstruction. One of the most curious questions about lignin chemistry is the polymerisation phase, which is still largely unclear. In this programme, both biochemical and molecular approaches are taken to elucidate and characterise some of the enzymatic steps in lignin biosynthesis.
Technical platforms
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Research 
